The present invention relates to a drive shaft for motor vehicles with shaft portions arranged one after the other in the longitudinal direction of the drive shaft. One shaft portion is a tubular shaft portion having a larger cross section and another shaft portion is a shaft portion having a smaller cross section. The shaft portion having the larger cross section is arranged, when the drive shaft is in an initial state, on one side of an annular transition region of the drive shaft and the shaft portion having the smaller cross section is arranged on the other side. The annular transition region includes a region wall that interconnects the shaft portion having the larger cross section and the shaft portion having the smaller cross section. The shaft portion having the larger cross section and the shaft portion having the smaller cross section are able to move relative to one another, under the action of a longitudinal force which acts on the shaft portion having the larger cross section and/or on the shaft portion having the smaller cross section in the longitudinal direction of the drive shaft and compresses the drive shaft starting from the initial state, in the longitudinal direction of the drive shaft and the region wall of the transition region between the shaft portion having the larger cross section and the shaft portion having the smaller cross section, forming a predetermined deformation point and/or a predetermined breaking point. The shaft portion having the smaller cross section has an insertion length which is arranged outside the shaft portion having the larger cross section when the drive shaft is in the initial state and extends in the longitudinal direction of the drive shaft and by which the shaft portion having the smaller cross section can be pushed into the shaft portion having the larger cross section when the drive shaft is compressed, thus deforming and/or breaking the region wall of the transition region arranged between the shaft portion having the larger cross section and the shaft portion having the smaller cross section. The shaft portion having the smaller cross section is guided inside the shaft portion having the larger cross section in the direction of movement when the shaft portion having the larger cross section and the shaft portion having the smaller cross section move relative to one another when the drive shaft is compressed.
The invention further relates to a method for manufacturing a drive shaft for motor vehicles, in which a plastically deformable tubular shaft blank is formed, thus forming a shaft portion having a larger cross section, a shaft portion having a smaller cross section that follows the shaft portion having the larger cross section in the longitudinal direction of the drive shaft when the drive shaft is in an initial state, and a transition region provided between the shaft portion having the larger cross section and the shaft portion having the smaller cross section. The transition region is produced to have a region wall that interconnects the shaft portion having the larger cross section and the shaft portion having the smaller cross section and that forms a predetermined deformation point and/or a predetermined breaking point under the action of a longitudinal force that acts on the shaft portion having the larger cross section and/or on the shaft portion having the smaller cross section in the longitudinal direction of the drive shaft and compresses the drive shaft starting from the initial state. The shaft portion having the smaller cross section is produced to have an insertion length which extends in the longitudinal direction of the drive shaft and is arranged outside the shaft portion having the larger cross section when the drive shaft is in the initial state and by which the shaft portion having the smaller cross section can be pushed into the shaft portion having the larger cross section in the event of a movement performed by the shaft portion having the larger cross section and the shaft portion having the smaller cross section relative to one another in the longitudinal direction of the drive shaft when the drive shaft is compressed, thus deforming and/or breaking the region wall of the transition region arranged between the shaft portion having the larger cross section and the shaft portion having the smaller cross section.
Motor vehicles, for example passenger vehicles, are often equipped with a drive shaft of the type mentioned above, which exhibit specific compressive behavior in the event of a crash under the action of an excess axial load caused by the crash, and thus convert impact energy into deformation energy, thereby absorbing said energy.
DE 10 2004 005 096 B3 discloses a generic drive shaft comprising a cylindrical tube portion having a relatively large cross section and a cylindrical tube portion having a relatively small cross section. The two tube portions are arranged one after the other in the longitudinal direction of the drive shaft and are interconnected by a transition portion that tapers from the tube portion having the larger diameter towards the tube portion having the smaller diameter. Inside the tube portions, a tubular piece is pushed, by a partial length, into the tube portion having the smaller diameter from the tube portion having the larger diameter. In the region of their mutual overlap, the tubular piece and the tube portion having the smaller diameter are fixed in place on one another by a press fit, which acts in particular in the axial direction. The part of the tubular piece arranged inside the tube portion having the larger diameter is widened in the radial direction with respect to the partial length of the tubular piece inserted into the tube portion having the smaller cross section so as to form a hollow cylinder, the external diameter of which is slightly smaller than the internal diameter of the tube portion having the larger diameter.
Under the action of an axial load on the drive shaft caused by an accident, the aforementioned drive shaft is compressed. The tube portion having the larger diameter and the tube portion having the smaller diameter move relative to one another in the longitudinal direction of the drive shaft, the tube portion having the smaller diameter being pushed into the tube portion having the larger diameter. The transition portion between the tube portion having the larger diameter and the tube portion having the smaller diameter enables the relative movement of the two tube portions. When the drive shaft is compressed, the transition portion is first deformed and then ultimately breaks, a bead that reduces the wall thickness of the transition portion forms a predetermined breaking point. Together with the tube portion having the smaller cross section, the tubular piece that is pressed onto the tube portion having the smaller diameter moves relative to the tube portion having the larger diameter. In the process, the hollow cylinder of the tubular piece arranged inside the tube portion having the larger diameter causes the tube portion having the smaller diameter to be guided in the tube portion having the larger diameter in the direction of the relative movement, and thereby prevents the drive shaft from buckling.